Four aperture radiator for illuminating main dish



March 1956 s. M. RANDALL FOUR APERTURE RADIATOR FOR ILLUMINATING MAIN DISH 4 Sheets-Sheet 1 Filed Jan. 50, 1963 BOTTOM VIEW INVENTOR GRANT M RANDALL 4 Sheets-Sheet 2 G. M. RANDALL FIG. 5b

FIG 5d FOUR APERTURE RADIATOR FOR ILLUMINATING MAIN DISH l7 w 28c f j 32c FIG. 50

March 15, 196

Filed Jan. 30,

FIG 5a ZGQI: 1 30 34A fi 38 March 15, 1966 G. M. RANDALL FOUR APERTURE RADIATOR FOR ILLUMINATING MAIN DISH Filed Jan. 30, 1963 4 Sheets-Sheet 3 I02 [I00 l6\ I |2.-C l4 SUM I DUPLEXER TRANSMITTER AzI UTH EL VATION TR TR TR I04 I06 I08 I I I I I MIxER MIXER MIXER LOCAL H6 H4 H2 OSC/JILLATOR INVENTOR. GRANT M. RANDALL F|G.7 ELEVATION AZIMUTH RANGE DIFFERENCE DIFFERENCE suM SIGNAL SIGNAL SIGNAL March 15, 1966 G. M. RANDALL 3,241,146

FOUR APERTURE RADIATOR FOR ILLUMINATING' MAIN DISH Filed Jan. 50, 1963 4 Sheets-Sheet 4 E36 4o V L940 E834 938 h A 734 E /E738 E34 38 INVENTOR.

GRANT M. RANDALL United States Patent 3,241,146 FOUR APERTURE RADIATOR FOR ILLUMINATING MAIN DISH Grant M. Randall, Whittier, Califi, assignor to North American Aviation, Inc. Filed Jan. 30, 1963, Ser. No. 254,387 4 Claims. (Cl. 343-779) This application is a continuation-in-part of patent application 119,771, Radar Antenna Microwave Connector, by Grant M. Randall, filed June 22, 1961, now abandoned.

This invention pertains to means for connecting a reflector-type microwave antenna to a source of microwave energy, and to a microwave detector; so that the same antenna can be used for transmitting and receiving microwave energy in a radar system.

It has been proposed to connect to a microwave reflector-type antenna by means of a four-aperture feedbridge. For example, see copending patent application Ser. No. 709,729 filed Jan. 16, 1958, now Patent No. 3,071,769, entitled Four Horn Feed Bridge, by Grant M. Randall, Stanley M. Kerber, and Dean B. Anderson.

The four-aperture feed-bridge terminates in a fouraperture radiator that is adapted to illuminate paraboloid reflectors of various configurations, for example; circular, rectangular, or elliptical. It is to be stressed that an important reason for using a four-aperture radiator is that a predetermined illumination pattern may be delivered to the reflector by adjusting the spacing and orientation of the four radiating apertures.

Some prior-art four-aperture radiators required narrow band slots, ridges, or the like (such as the structure set forth in the above application) to extract azimuth and elevation information from the returned signal or echo; and these devices tend to be a complex mechanical structure.

Other prior-art devices, for example the structure disclosed in Ashby Patent 2,956,795, used a turn-around that directed energy at the concave surface of the reflector. However, since the Ashby device used a duo mode concept of energy transmission, the turn-around was therefore limited by the fact that it could be curved in only one given direction. This limitation limited the position of the tum-around apertures to a limited number of locations relative to the focal point of the dished reflector; and thus produced a limited number of radiation and reception patterns for the radar system.

Other radar transmission-and-reception structures, as exemplified by Hanson Patent 2,973,487 and Smith Patent 2,759,154 used straight and flaring horn-type mouths, respectively, rather than large dished reflector antennas. These arrangements lost the advantages of the paraboloid reflector-type antennas, and were therefore less efficient.

The instant invention overcomes the disadvantages of the prior-art arrangements in that it uses the high-efficiency dished antenna, and is still a simple mechanical structure. Basically, it uses four waveguides and four turn-arounds, each adapted to transmit microwave energy only in the maximum efiiciency TE mode. This single-mode transmission permits the turn-arounds to be curved or twisted so that their apertures may be placed at any desired orientation and/or position relative to the focal point of the paraboloid reflector-type antenna. This concept produces transmission and reception patterns that may have symmetrical wide angles or small angles, unsymmetrical distributions, or even skewed distributions; depending upon the desired shape, size, and aperture of the reflector-type antenna, and the position of the openings of the turn-arounds.

3,241,146 Patented Mar. 15, 1966 Each of the waveguides and turn-arounds of this invention transmits energy in only the principal or fundamental (TE mode. It is proposed by this invention that radar energy received from a target, be channeled by each pair of adjacent waveguides into devices such as an H-plane hybrid (see Patent No. 2,956,275 to'R. M. Ashby) and an E-plane hybrid or folded waveguide T wherein azimuth, elevation, and range information is extracted.

It is contemplated by this invention to connect rec tangular waveguide means between a microwave generator and a microwave antenna reflector for illuminating a distant target with microwave energy, said rectangular waveguide means having a four-aperture radiator including microwave turn-arounds for illuminating an antenna reflector with transverse electric energy. The Waveguide means, utilized in this invention, has four separate identical rectangular guides on a first end, connected to the four-aperture radiator, with each of the four guides connected to a separate aperture. The four rectangular guides which are connected to the four-aperture radiator are each adapted to support the TE mode.

The second end of the guide means has two identical rectangular stacked guides, stacked along the narrow dimension of the guide means, with each guide having its wide dimension across the wide dimension of the guide means. Each of the two identical stacked guides is adapted to support both one and two halflwave variations in field density (TE and TE modes) across their broad transverse dimension.

In the preferred embodiment the guides are formed within the waveguide means by a pair of mutually perpendicular septums which extend along the guide means parallel to the direction of propagation, and bisecting the two transverse dimensions of the guide means parallel and perpendicular to the electric field respectively. The septum which bisects the narrow transverse dimension of the guide means is adapted to separate the previously mentioned stacked guides, while both septums cooperate to form the above mentioned tour guides. Appropriate receiver means are connected to the waveguide means through H-plane and E-plane hybrid Ts to extract azimuth, range, and elevation information. Appropriate range detecting receivers are connected to the second end of the waveguide means to be utilized to measure the time between the transmitted pulse and the received echo.

It is an object of this invention to provide means for producing desired transmission and radiation radar patterns.

It is another object of this invention to detect the position of a target relative to a radar system.

It is another object of this invention to provide simpler and more compact microwave means to propagate, detect, and separate monopulse signals which are a measure of the angle and range between a radar antenna and its target.

It is also an object of this invention to propagate, detect, and separate microwave signals which are a measure of the azimuth angle, the elevation angle, and the range of a radar target.

The attainment of these and other objects will become apparent from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a side view, partially in section, of the device of this invention;

FIG. 2 is a bottom view of the device of this invention;

FIG. 3 is a view, partially in section, taken at 33 in FIG. 1;

FIG. 4 is a sectional view taken at 4-4 in FIG. 1;

FIGS. 5a to 5e show a series of views partially in section showing the possible spatial orientations of the outputs, taken at 55 in FIG. 1;

FIG. 6 is a view, partially in section, taken at 66 in FIG. 1;

FIG. 7 is a block diagram of a typical radar system employing the device of this invention;

FIG. 8 is a symbolic diagram of a typical relation between the electric field amplitudes in the four waveguides attached to the four-aperture radiator when a target is on the boresight axis of the antenna;

FIG. 9 is a symbolic diagram of a typical relation between the electric field amplitudes in the four waveguides attached to the four-aperture radiator when there is an elevation relation between the target and the boresight axis of the antenna;

FIG. 10 is a symbolic diagram of a typical relation between the electrical field phases in the four waveguides attached to the four-aperture radiator when there is an azimuth relation between the target and the boresight axis of the antenna.

In FIGS. 1 and 2 is shown a dual-purpose monopulse device 16. In order to direct microwave energy toward a target, energy enters at end 14, travels along device 16, thru turn-arounds (best seen in FIG. 2), leaves radiating means 12 (which is at the focal point of the reflector), and illuminates antenna reflector 10; which thereupon reflects the microwave energy toward a target. In order to receive microwave energy from the target, the energy that impinges onto reflector 10 is focused onto radiating means 12, travels thru turn-arounds 20, is transmitted along device 16, and leaves at 58, 62, and 14; from whence it enters suitable utilization devices that resolve the received energy into range and angular information of the target. Thus, in one usage, reflector 10 is illuminated by the four-apertured radiating means 12; and in another usage it reflects received energy into the fourapertured radiating means 12. Since reflector 16 is adapted to illuminate a distant target with microwave energy, and to gather reflected microwave energy from the distant target, the reflector 10 may have any of the curvatures and shapes known to the art to help create the desired radiation and reception pattern. Moreover, in accordance with the instant invention, the positions of the openings of the turn-arounds 20 may be positioned and oriented to aid in the creation of the desired radiation and reception pattern.

The coordinates of the radar system are displayed in FIGS. 1 and 2. The Z-axis is the optical, or boresight axis, of the radar antenna. A first component angular measurement, denoted the azimuth angle of the target, is measured by rotation about the X-axis. A second component angular measure, denoted the elevation angle of the target, is measured by rotation about the Y-axis. It is apparent that the designations elevation and azimuth are arbitrary, depending upon the orientation of the subject device.

At this point it will be helpful to understand the way, or mode, that energy travels through a rectangular waveguide. If a rectangular duct, or waveguide, has one dimension that is slightly greater than 1 half-wavelength, this means that only 1 half-wavelength can fit into this dimension. If the other dimension of the rectangular Waveguide is slightly less than 1 half-wavelength, this means zero half-wavelengths can fit into this dimension. Thus the principal mode of transmission of a waveguide 1 this size is designated as a TE mode; the subscripts 1 and zero indicating the number of half-wavelengths that fit into the dimensions of the rectangular waveguide.

If the waveguide were twice as wide as above, but of the same height, the wide dimension would support 2 half-wavelengths, while the narrow dimension would still support zero half-wavelengths. This double-width waveguide would support a TE mode, as well as a TE mode and would be called a duo-mode waveguide.

With the above explanation in mind, the main waveguide, at 14 in FIGS. 1 and 2, is a single rectangular passage which is slightly more than half a wavelength high, and less than half a wavelength wide. It will therefore propagate microwave energy only in its principal, or TE mode. In regions 19 and 22, the device is heightened, and is divided by a vertical septum 18, as shown in FIGS. 1 and 3, resultingas shown in FIG. 6in two primary waveguides 44 and 46, each of which is 2 half-wavelengths high and less than A wavelength wide. Thus, primary waveguides 4-4- and 46 are adapted to support both TE and TE modes of propagation in transition region 22 only of FIGS. 1 and 3.

A horizontal septum, 24, of FIG. 1, divides each of the two primary waveguides 44 and 46 into pairs of independent secondary waveguides 34, 36 and 38, 40 as shown in FIG. 5a; each secondary waveguide 34, 36, 38, and 40 being one-half wavelength high and less than A; wavelength wide. Thus, the secondary waveguides 34, 36, 38, and 40 can support only the T13 mode. The independent secondary Waveguides are formed by the outer walls of device 16 and the pair of perpendicular septums 18 and 24. Each of the four secondary waveguides 34, 36, 38, and 40 is connected to an individual turn-around portion 29 as illustrated in FIGS. 2 and 4, and which are also dimensioned to support only the TE mode. The drawings show 180 degree turn-arounds, so that the turnaround openings 26, 28, 3t), and 32 of FIG. 5a form the four-apertured radiator means 12 that faces the concave surface of reflector 10.

A property of a TE mode waveguide is that it may be twisted or curved in almost any desired manner, whereas this is not true of a duo-mode waveguide.

Since the turn-arounds conduct only in the T13 mode, they may be curved and twisted in any desired degree and direction, so that the apertures 26, 28, 30, and 32 may be positioned as shown in FIGS. Sa-Se, or any other arrangement, to provide the desired polarization, and transmission and radiation patterns.

As shown in FIG. 5a the radiating apertures 26, 28, 30, and 32 are positioned in a predetermined configuration, preferably adjacent to and symmetrically about the focal point of reflector 10, in order to illuminate reflector 10 with a desired illumination pattern. The locations of apertures 26, 28, 30, and 32 shown in FIG. 511 has the characteristic that the openings 26, 28, 30, and 32 are as close as possible to the focal point of the concave reflector 10. It is of course an impossibility for the four apertures 26, 28, 30, and 32 to all be at the focal point of reflector 10; but in actuality the apertures of FIG. 5a are so close that the ideal conditions are substantially realized. In FIG. 5a the openings 26, 28, 30, and 32 have the same orientation as the waveguides; whereas in FIG. 5b they are rotated degrees, which changes the polarization. FIGS. 50 and 5d show opening locations that place the openings farther apart in the vertical direction; and FIG. 5e shows the openings skewed with respect to the secondary waveguides. Thus, the exemplary positions and orientations illustrated in FIG. 5 provide various combinations of angularly squinted and parallel horns, and c0ntrol of the plane of polarization.

As previously explained, for transmit-ting the radar signal, energy is applied to the main waveguide 14 of device 16; whereupon it traverses the device and emerges at the four-apertures 26, 28, 30, and 32 of radiating means 12. If, as shown in FIG. 5a, these apertures are clumped around the focal point of antenna reflector 10, and if rc flector 10 is a paraboloid, the radar signal is transmitted in a relatively narrow pencil-like beam. Under some conditions it is desirable that other than pencil-like beams be used; and the instant invention perimts the four radiating apertures to form patterns that may be square, rectangles, or skewed arrangements in order to help provide these other patterns.

Radar energy that is reflected by a target on the boresight axis of reflector produces equal signals in secondary waveguides 34, 36, 38, 40; these signals being combined at 14. The combined information at 14 is used to measure the range to the target. The sum of thereceived signals, at 14 is connected, as shown in FIG.- 7, thru duplexer 102, TR device 108, mixer 112, and ampliher 118. The time occurence of the received signals relative to a transmitted pulse may then be employed (by means not shown) to generate a range signal.

In order to measure the elevation angle of the target, a microwave comparison device connection, such as an H- plane hybrid T 42 shown more particularly in FIG. 6 is connected to device 16 in the region 22.

The following somewhat simplified explanation will clarify how elevation angle signals are obtained. Assume that the target is directly above the boresight axis Z of the antenna system. As a result, the pair of lower secondary waveguides (36, 40, of FIG. 5) will receive reflected signals of a somewhat different amplitude than will the pair of upper secondary waveguides 34, 38; although each secondary waveguide 34, 36, 38 and 40 will transmit the energy only in the TE mode. In the region 22 of device 16 (of FIG. 1) the horizontal septum 24 ends; and the vertical septum 18 creates two primary waveguides 44 and 46, as shown in FIG. 6; each adapted to support duo-mode TE and TE propagation in the transition region 22. Rectangular apertures 48 and 50 are positioned in the central region of primary waveguides 44 and 46, respectively.

The energy in the lower portion of the primary waveguide 44, since it originated in lower secondary waveguide 36, has a somewhat different amplitude than the energy in the upper portion of primary waveguide 44, since that energy originated in the upper secondary Waveguide 34. As a result, a TE mode appears in primary waveguide 44, which causes a difference in voltage to appear across aperture 48. This difference voltage, which is a function of the TE mode, excites a TE mode in connecting waveguide 52. This TE mode is fed into elevation output waveguide 58.

Similarly, a difference voltage appears across aperture 50; and excites a T15 mode thru connecting waveguide 54. Combining T 56 sums these two TE modes of connecting waveguides 52 and 54. Hence, a difference signal indicative of target elevation angle occurs at the output of elevation output waveguide 58. The energy in elevation output waveguide 38, as shown in FIG. 7, is connected thru TR device 104, mixer 116, and amplifier 122 to generate a signal which is a measure of the elevation angle, or the angular position, about the Y-axis.

In order to measure the azimuth angle of the target, a microwave signal comparison device such as an E-plane hybrid T 68, shown more particularly in FIG. 3, is connected at the stepped section of septum 18. Again, a somewhat simplified explanation will clarify the operation. If the target is off to one side of the boresight axis Z, the pair of secondary waveguides 34, 36 of FIG. 5 will receive the reflected signal at a somewhat different time (phase) than will the pair of secondary waveguides 38, although each secondary waveguide 34, 36, 38, and 40 will transmit the energy in the TE mode. The continuous vertical septum 18 keeps these differently-phased TE signals separated until they reach the stepped section of septum 18 at T 60, as shown in FIG. 3. Here the differently-phased TE signals combine to produce a difference voltage across the slot 61, which produces a corresponding TE mode in azimuth output waveguide 62.

Azimuth output waveguide 62, adapted to support only TE mode microwaves, is connected, as shown in FIG. 7, to TR device 106, mixer 114, and amplifier 120 to generate a signal which is a measure of the azimuth angle, or the angular position, about the X-axis.

Summarizing, a target above or below the boresight axis of reflector 10 produces different-amplitude signals in secondary waveguides 34, 36 and 38, 40; and excites the TE mode in the transition region 22. The information is extracted by H-plane hybrid T 42 which generates a signal in elevation output waveguide 58; which signal is a measure of the elevation angle about the Y-axis of the device. Similarly a target to the right or the left of the boresight axis of reflector 10 produces differentiallyphased signals in the TE mode between waveguides 44 and 46. This information is extracted by E-plane hybrid T 60, and generates a signal in azimuth output waveguide 62; and is a measure of the azimuth angle about the X-axis.

As shown in FIG. 7, when radar energy is to be transmitted toward the target, energy is introduced from transmitter 100, passed thru duplexer 102 to device 16 at 14, and, as previously explained, is divided at septum 18, and redivided at septum 24, to cause equal amounts of TE energy to be emitted mutually in-phase from apertures 26, 28, 3t), and 32. The energy thus illuminates reflector 10, which directs it toward the target.

Local oscillator generates a signal which tracks the signal of transmitter 100. Oscillator 1% is connected to mixers 112, 114, and 116 which produce intermediatefrequency signals by the well know heterodyning principle.

A further explanation of the operation of the device of this invention is given in connection with FIGS. 8-10. When the target is on the boresight or Z-axis of the antenna 10, equal reflected signals reach apertures 26, 28, 30, and 32. The relation of the electric fields in secondary waveguides 34, 36, 38, and 40 is shown in FIG. 8 at E34, E E and E respectively. These equal-amplitude signals are summed, and appear at 14.

When the target is above the boresight or Z-axis (i.e., when it has an elevation angle), the amplitude of the signals in waveguides 34, 36, 38, and 40 are shown in FIG. 9 by vectors E 4, E 6, E and E of which the upper vectors E and E are smaller than the lower vectors E and E (due to cooperation of the reflector with the array of apertures).

The intensity of E may be considered as the difference between a given-sized large signal E and a given-sized small signal E Similarly, E may be considered as the difference between a large signal E and small signal E Signal E may be considered as the sum of signals E and E and signal E may also be considered as the sum of the signals E and signal E Signals E E E and E are equal in amplitude, and are summed at 14 to provide range information. Signals E E E and E are also equal in amplitude, and H-plane hybrid T 42 extracts a signal that is proportional to their amplitude. The resultant difference signal at T 42 is thus a measure of the elevation angle about the Y- axis of the device; and its direction indicates whether the target is above or below the boresight axis.

When the target is to one side (horizontally) of the Z or boresight axis, the return signals in waveguides 34, 36, 38, and 40 have a phase relation which is shown by the vector or phasor diagram of FIG. 10. Signals E E E and E represent the signals present in waveguides 34, 36, 38, and 40, respectively. In this case vectors E E E and E may be considered to have components E E E and E respectively, and quadrature components E E E and E respectively. The quadrature components E E E and E are extracted thru T 60 to generate a difference signal which is a measure of the angle about the X-axis (azimuth angle) of the target. Signals E E E and E are summed at 14, and are used, as previously described, to indicate the range of the target.

It will be noted that the disclosed device has a constant width, and two simple changes in height; thus leading to a simple mechanical structure. This structure is achieved as follows:

Referring to FIG. 5a, each secondary Waveguide 34, 36, 38, and 40 has a vertical dimension slightly greater than 1 half-wavelength, and has a horizontal dimension of less than A of that wavelength. Thus, each secondary waveguide can transmit energy only in the TE mode.

At the point where the horizontal septum 24 terminates, the horizontal dimension of the remaining waveguides (designated as 44 and 46 in FIG. 6) is still the wavelength, while the vertical dimension is slightly greater than 2 half-wavelengths; and remaining waveguide sections 44 and 46 will now support both the TE and TE mode the latter of which mode activates the elevation output T 42.

Just past transition region 22 in FIG. 3, the device maintains the same horizontal dimension, while being reduced in the vertical direction, so that it can no longer support the TE mode, but can still support the TE mode. Thus, the TE mode exists only in the transition region 22.

Referring now to FIG. 2, it will be seen that the two primary waveguides merge where stepped septum 18 ends, to form a single main waveguide 14. If the horizontal dimension of each of the two primary waveguides 44 and 46 had been equal to A a wavelength, as was usually the case in prior-art structures, waveguide 14 would now be 1 half-wavelength wide, and l half-wavelength high; and would be able to support a TE mode. Since this TE mode of energy propagation is undesirable, primary waveguides 44 and 46 are formed somewhat narrower than A of a wavelength. Thus, when primary Waveguides 44 and 46 merge to form the main waveguide 14, the resulting waveguide cross-section is therefore not square in shape, but is half a wavelength high (in the vertical direction), and somewhat smaller than /2 a wavelength wide (in the horizontal direction), and is therefore capable of supporting only the TE mode. The stepped ending of septum 18 provides a means whereby the narrow horizontal dimension of waveguides 44 and 46 can couple to output T 60, and can yet be small enough so that the main waveguide is adapted to support only the TE mode. This arrangement permits device 16 to have a constant width along its entire length, and thus a simplified structure which is cheaper and simpler to manufacture. It should also be noted that the secondary waveguides are independent, and do not have any top-wall, or side-wall coupling slots.

The device of this invention efliciently resolves the information received from a target into range, elevation, and azimuth information; using a minimum amount of microwave structure, since it comprises simple, independent, rectangular waveguides involving a minimum of metal work. Moreover, it permits the four apertures to be conveniently spaced, oriented, and positioned. Further, the device of this invention is a broadband device, while prior known resolving structures for fourhorn feed bridges utilized band filters, or the like.

Although the device of this invention has been described in detail, it is not intended that the invention should be limited by the description, but only in accordance with the spirit and scope of the appended claims.

I claim:

1. In a radar antenna system, the combination comprising an antenna feed system having four rectangular waveguides adapted to transmit energy only in the TE mode; and

180 degree turn-around means adapted to conduct energy only in the TE mode, positioned at the end of each said waveguides, for causing the energy to 8 be directed in the opposite direction, the orientation of the openings of said degree TE turn-arounds being skewed relative to the orientations of the waveguides.

2. An antenna system comprising in combination a reflector;

a plurality of rectangular waveguides adapted to transmit energy only in the TE mode; and

.a rectangular turn-around positioned at the end of each said waveguide, the rectangular openings of said turnarounds having mutually skewed orientations and being located adjacent the focal point of said reflector and aimed at said reflector.

3. The radar combination comprising a concave reflector having a suitably-shaped outline;

a set of four secondary waveguides adapted to transmit energy only in the TE mode, said waveguides being positioned along the axis of said reflector;

a TE mode twisted, rectangular turn-around positioned at the end of each said waveguide remote from said reflector, the open ends of said turn-arounds facing the concave surface of said reflector and having mutually skewed orientations, said TE mode turn-arounds being positioned at desired orientations and locations with respect to the focal point of said reflector.

4. A radar device comprising in combination a concave reflector having an axis of symmetry and a focal point;

radar energy conducting means positioned along said axis of symmetry, comprising a main rectangular waveguide adapted to conduct only in the TE mode;

first septum means, positioned to bisect said main waveguide, for forming two rectangular primary waveguides, a first end of said first septum being stepped and terminating at said main waveguide;

second septum means, shorter than said first septum, positioned orthogonally to said first septum, for forming two primary waveguides into four rectangular secondary waveguides adapted to conduct only in the TE mode, a first end of said second septum means being directed toward said main waveguide;

a TE mode twisted, rectangular turn-around positioned at the outer end of each said secondary waveguides, the rectangular open ends of said TE turnarounds having mutually skewed orientations and being positioned adjacent said focal point to illuminate the concave surface of said reflector, and to receive signals from said reflector;

an E-plane hybrid T positioned at the stepped end of said first septum; and

an H-plane hybrid T positioned on either side of said radar conducting means between the adjacent ends of said two septum means.

References Cited by the Examiner UNITED STATES PATENTS 2,929,059 3/1960 Parker 343l6 2,956,275 10/1960 Ashby 343-161 3,071,769 1/1963 Randall et al. 343-I6.1

ELI LIEBERMAN, Acting Primary Examiner.

CHESTER L. JUSTUS, Examiner. 

1. IN A RADAR ANTENNA SYSTEM, THE COMBINATION COMPRISING AN ANTENNA FEED SYSTEM HAVING FOUR RECTANGULAR WAVEGUIDES ADAPTED TO TRANSMIT ENERGY ONLY IN THE TE10 MODE; AND 180 DEGREE TURN-AROUND MEANS ADAPTED TO CONDUCT ENERGY ONLY IN THE TE10 MODE, POSITIONED AT THE END OF EACH SAID WAVEGUIDES, FOR CAUSING THE ENERGY TO BE DIRECTED IN THE OPPOSITE DIRECTION, THE ORIENTATION OF THE OPENINGS OF SAID 180 DEGREE TE10 TURN-AROUNDS BEING SKEWED RELATIVE TO THE ORIENTATIONS OF THE WAVEGUIDES. 